refactor: server code (#2545)

+ Remove duplicated await
+ Replace some legacy codes with ES6
+ Fix some of eslint problems

server/modules/rendering/markdown-plantuml/renderer.js

@@ -74,13 +74,8 @@ module.exports = {
             continue
           }
 
-          var closeMarkerMatched = true
-          for (i = 0; i < closeMarker.length; ++i) {
-            if (closeMarker[i] !== state.src[start + i]) {
-              closeMarkerMatched = false
-              break
-            }
-          }
+          const i = closeMarker.findIndex(item => item !== state.src[start + i])
+          const closeMarkerMatched = i !== -1
 
           if (!closeMarkerMatched) {
             continue
@@ -112,7 +107,7 @@ module.exports = {
           altToken
         )
 
-        var zippedCode = encode64(zlib.deflateRawSync('@startuml\n' + contents + '\n@enduml').toString('binary'))
+        const zippedCode = encode64(zlib.deflateRawSync('@startuml\n' + contents + '\n@enduml').toString('binary'))
 
         token = state.push('uml_diagram', 'img', 0)
         // alt is constructed from children. No point in populating it here.